1. Field
This disclosure relates to production of hard copy output using clustered devices, more particularly to a method for delivering the data for hard copy output using multicasting.
2. Background
It is possible to produce one large copying or printing task on several devices. A host application assigns a portion of a print or copy task to one of several devices. The several devices are connected via a network. A group of such devices are referred to as a cluster. The devices may be printers, copiers or printer/copiers, as well as other combinations of functions, such as printer/copier/fax, etc. Regardless of the individual capabilities of the devices, they are part of a cluster and so will be referred to as clustered devices. Additionally, this invention relates to production of hard copy output, so the devices may also be referred to as printers, which will include copiers and fax machines within its definition.
Similarly, the task which the clustered devices are assigned may be a print job, where the original data to be produced as hard copy output is generated from an application running on a computer. Alternatively, it may be a copy job, where the data to be produced as hard copy is generated by a scanning device. The scanning device may be part of a copying apparatus, such as a copier, or may be a stand alone. In either case, however, the goal is to produce a hard copy output of the data. For that reason, these tasks will be referred to as print jobs, regardless of the source of data to be rendered by the print engine.
Currently, a large job that is to be produced by clustered devices must be transmitted to each device individually in most local area networks (LANs) such as an Ethernet. The Ethernet network is a simple bus structure where every device on the network sees all of the information transmitted over the network. However, only the device to which that information is addressed actually acquires the data to act upon it.
One variation from this approach is discussed in U.S. Pat. No. 4,493,049, issued Jan. 8, 1985. In this approach, print data is converted into an output marker bit stream and saved to disc. The stored bit streams are then retrievable from the disc by other devices. However, the step of saving to disc adds another layer of complexity not necessary in the current state of networks. Current networks do not suffer from the problems of lost data or multiple accesses to the same data this approach was designed to overcome. Therefore, the extra step is no longer necessary and is not an efficient solution to the problem. Further, for the data to be accessed by multiple devices, the data still has to be transferred across the network as individual data streams, contributing to the problems discussed above.
Some devices vary from the point to point approach discussed above, such as network sniffers. Sniffers glean information from the network typically by recording all traffic for later analysis. However, for the most part, devices on networks similar to the Ethernet require data to be addressed to them specifically. An example of this is shown in prior art FIG. 1.
The host application, server 10 in this example, sends data to each of the printers 12a–12n. Each printer requires the data to be individually addressed, so the arrows represent the same print job being sent to each printer. This results in a high volume of repeated traffic.
One area in which a solution may lie is multicasting. A multicast is a broadcast of data to several devices on a network. The addressing is handled in such a way that the data is received by several devices, although it was only sent once. Several patents address various issues with multicasting.
Allocation of addresses for multicast participants is addressed in U.S. Pat. No. 5,835,723, issued Nov. 10, 1998. U.S. Pat. No. 5,517,494, issued May 14, 1996, addresses multicasting protocols in network routers. Neither of these approaches discloses a solution to the clustered printing issues discussed above.
U.S. Pat. No. 5,727,002 addresses the problems of transmission loss in multicast transmissions. The system disclosed provides for acknowledgements to be transmitted across a frame relay network to confirm reception of frames sent by multicasting. While this solution addresses the reduction in transmission by multicasting, it does not provide any relief to the lack of multicasting availability for clustered printers.